The present invention relates to asynchronous transmission mode (ATM) mobile radio systems.
In mobile radio systems it is important that the radio spectrum be used efficiently. Known techniques by which this efficiency can be improved require that mobile terminals or units frequently change the base station or base stations to which they are affiliated (i.e., through which they communicate). This can impose stringent requirements on switching times in the fixed network infrastructure if breaks in communication due to reaffiliation are to be kept short. Typically, the network part of a mobile system consists of base stations connected to a mobile network interface unit (MNIU), which in turn is connected to a fixed network. The MNIU is the point of interconnection between the mobile network and the fixed network for as long as a call is being handled by one of the base stations in its area of responsibility.
It will be appreciated that the term "call" used throughout the specification also includes the set up of a connection, e.g., for signalling purposes.
In networks which use or handle ATM data, the data transmitted in such networks is subdivided into small packets of data, known as cells. The cells generally consist of 48 octets of user data and 5 octets of header information.